Contaminants, for example ice, rain, water droplets, sand, smoke particles, dust particles, or other contaminants that may accumulate on external surfaces of aircraft, particularly aerofoils and other aerodynamic surfaces, can seriously affect the aerodynamic performance, in particular the lift and drag characteristics, of the aircraft, and can also change the weight and centre of gravity of the aircraft.
For laminar wings, relatively minor wing contamination or flow disturbances (depending on Reynolds number) can produce a complete loss of laminar flow on the wing surfaces, and the loss of laminar flow results in drag penalties and to deterioration of maximum lift. However, strong contamination with the ensuing more significant flow disturbances, may go beyond simple loss of laminar flow and may result in fully turbulent flow on the wing surfaces. For turbulent wings, increase of flow disturbances produce a further deterioration of maximum lift and a further increase of drag penalties. If contamination and the flow disturbances continue to increases, the wings may become unflyable.
De-icing apparatus are known and operate by periodically removing ice after it accumulates, by thermal, chemical or mechanical means. Anti-icing apparatus are also known, and attempt to prevent the formation of ice in the first place.
Thermal anti-icing systems include bleed air systems that use exhaust gas from the aircraft to heat air which is circulated in ducts running along areas of the aircraft where it is wished to prevent the ice build up, preventing the ice from forming or melting the same. Electro-thermal systems use electrically powered heating elements on these areas of the aircraft.
Other anti-icing systems use a chemical such as antifreeze, injected to the ice-prone surfaces to prevent the ice from forming. For example, by way of general background, in U.S. Pat. No. 5,322,246 a chemical or thermal deicing or running wet anti-icing device is located in or on the airfoil upstream of an aft facing step situated across the span of a single element airfoil, and causes water to run back towards the step. The step suddenly reduces the thickness of the airfoil chord section, which causes a disturbance in the boundary layer across the span of the airfoil downstream of the step. According to the patent, the aforementioned disturbance causes runback water to form droplets and be blown clear of the airfoil surface downstream of the step.
Known anti-icing systems are generally directed to single aerofoil element, and are not directed to wings based on two-element slotted aerofoils, in particular to the accumulation of ice, rain or other contaminants on the second element of such aerofoils.
Solutions for dealing with other types of contaminants with respect to aerofoils or wing surfaces are not generally known or used.